ENZYMES.pdf

1. Oxidoreductase I. GENERAL PROPERTIES - is an enzyme that catalyzes an oxidation–reduction...

1. Oxidoreductase I. GENERAL PROPERTIES - is an enzyme that catalyzes an oxidation–reduction reaction. ENZYME - An enzyme is a compound, usually a protein, that catalyzes a biochemical reaction. ENZYME STRUCTURE 1. Simple Enzyme 2. Transferase - is an enzyme composed only of protein - is an enzyme that catalyzes the transfer of a (amino acid chains). functional group from one molecule to 2. Conjugated enzyme another. Two major subtypes of transferases - is an enzyme that has a nonprotein part in are trans-aminases and kinases. addition to a protein part. Apoenzyme is the protein part of a conjugated enzyme. A holoenzyme is the biochemically active conjugated enzyme produced from an apoenzyme and a cofactor A cofactor is the non protein part of a conjugated enzyme. II. CLASSIFICATION OF ENZYMES 3. Hydrolase - is an enzyme that catalyzes a hydrolysis reaction in which the addition of a water molecule to a bond causes the bond to break.  4. Lyase ENZYME- SUBSTRATE COMPLEX - is an enzyme that catalyzes the addition of a - Is the intermediate reaction species that is group to a double bond or the removal of a formed when a substrate binds to the active group to form a double bond in a manner site of an enzyme. that does not involve hydrolysis or oxidation. LOCK-AND-KEY MODEL - The active site in the enzyme has a fixed, COO- COO- rigid geometrical conformation. Only | fumarase | substrate with a complementary geometry C—H + H2O HO—C—H can be accommodated at such a site, much || | as a lock accepts only certain keys. H—C H—C—H | | COO- COO- Furminate L-malate 5. Isomerase - is an enzyme that catalyzes the isomerization (rearrangement ofatoms) of a substrate in a reaction, converting it into a molecule isomeric with itself. COO- COO- | | INDUCED-FIT MODEL H—C—OH H—C—O—P - Allows for small changes in the shape or | | geometry of the active site of an enzyme to CH2O—P CH2OH accommodate a substance. 3-Phosphoglycerate 2-Phosphoglycerate - Induced-fit model is a result of the enzyme’s flexibility; it adapts to accept the incoming 6. Ligase substrate. - is an enzyme that catalyzes the bonding together of two molecules into one with the participation of ATP. IV. ENZYME SPECIFICITY III. MODELS OF ENZYME ACTION ENZYME SPECIFICITY - Is the extent to which an enzyme’s activity is restricted to a specific substrate, a specific group substrate, a specific type of chemical bond, or a specific type of chemical reaction. TYPES OF ENZYME SPECIFICITY 1. ABSOLUTE SPECIFICITY - the enzyme will catalyze only one reaction. - Catalase is an enzyme with absolute specificity. ENZYME ACTIVE SITE It catalyzes the conversion of hydrogen peroxide - Is the relatively small part of an enzyme’s (H2O2) to O2 and H2O. Hydrogen peroxide is structure that is actually involved in the only substrate it will accept. catalysis.  2. GROUP SPECIFICITY - the enzyme will act only on molecules that have a specific functional group, such as hydroxyl, amino, or phosphate groups. - Carboxypeptidase is group specific, it cleaves amino acids, one at a time, from a carboxyl end of a peptide chain. 3. LINKAGE SPECIFICITY - the enzyme will act on a particular type of chemical bond, irrespective of the rest of the molecular structure. - Phosphatases hydrolyze phosphate-ester bonds ENZYME CONCENTRATION in all types of phosphate esters. - Because enzymes are not consumed in the - Linkage specificity is the most general of the reactions they catalyze, the cell usually common specificities. keeps 4. STEREOCHEMICAL SPECIFICITY - the enzyme - The number of enzymes is low compared will act on a particular stereoisomer. with the number of substrate molecules. - L-amino acid oxidase will catalyze the oxidation This is of the L-form of an amino acid but not the - efficient; the cell avoids paying the energy D-form of the same amino acid. costs of synthesizing and maintaining a large - work force of enzyme molecules. V. FACTORS THAT AFFECT ENZYME ACTIVITY VI. ENZYME INHIBITION ENZYME ACTIVITY - Is a measure of the rate at which an enzyme covers substrate to products in a biochemical ENZYME INHIBITOR reaction. - Is a substance that slows or stops the normal catalytic function of an enzyme by binding TEMPERATURE to it. - Is a measure of the kinetic energy (energy of motion) of molecules. At higher REVERSIBLE COMPETITIVE INHIBITION temperatures, molecules are moving faster - Is a molecule that sufficiently resembles an and colliding more frequently. enzyme substrate in shape of charge - Optimum Temperature is the temperature distribution that it can compete with the at which an enzyme exhibits maximum substrate for occupancy of the enzyme’s activity. active site. - For human enzymes, the optimum temperature is around 37°C, normal body temperature. PH - The pH of an enzyme’s environment can affect its activity. The charge on acidic and basic amino acids located at the active site depends on pH. REVERSIBLE NONCOMPETITIVE - Optimum pH is the pH at which an enzyme INHIBITION exhibits maximum activity. - Is a molecule that decreases enzyme activity - Pepsin in the stomach functions best at 2.0 by binding to a site on an enzyme other pH. Trypsin in the small intestine functions than the active site. best at 8.0 pH. SUBSTRATE CONCENTRATION - When the concentration of an enzyme is kept constant and the concentration of substrate increases, the enzyme activity pattern shown in the figure below is obtained. - This activity pattern is called a saturation curve.  REVERSIBLE INHIBITION VIII. COVALENT MODIFICATION OF ENZYMES (UNCOMPETITIVE) - is a molecule that inactivates enzymes by forming a strong covalent bond to an amino COVALENT MODIFICATION acid side-chain group at the enzyme’s active - a process in which enzyme activity is altered site. by covalently modifying the structure of the - In general, such inhibitors do not have enzyme through attachment of a chemical structures similar to that of the enzyme’s group to or removal of a chemical group normal substrate. from a particular amino acid within the - Will only bind to the substrate if it is already enzyme’s structure. binded. VII. REGULATION OF ENZYME ACTIVITY PHOSPHORYLATION - The process of addition of the phosphate group to the enzyme ALLOSTERIC ENZYMES - Is an enzyme with two or more protein chains (quaternary structure) and two kinds DEPHOSPHORYLATION of binding sites (substrate and regulator). - the removal of the phosphate group from the - Substances that bind at regulatory sites of enzyme. allosteric enzymes are called regulators. - This phosphorylation/dephosphorylation - The binding of a positive regulator process is the off/on or on/off switch for the increases enzyme activity; the shape of the enzyme. For some enzymes the active active site is changed such that it can more (“turned-on” form) is the phosphorylated readily accept substrates. version of the enzyme; however, for other enzymes it is the dephosphorylated version FEEDBACK CONTROL that is active. - is a process in which activation or inhibition of the first reaction in a reaction sequence is PROTEIN KINASES controlled by a product of the reaction - Effect the addition of phosphate groups and sequence. phosphatases catalyze removal of the phosphate groups. Usually, the phosphate group is added to (or removed from) the R group of a serine, tyrosine, or threonine VIII. PROTEOLYTIC ENZYMES AND ZYMOGENS amino acid residue present in the protein (enzyme). PROTEOLYTIC ENZYME GLYCOGEN PHOSPHORYLASE - is an enzyme that catalyzes the breaking of - An enzyme involved in the breakdown of peptide bonds that maintain the primary glycogen to glucose is activated by the structure of a protein. addition of a phosphate group. ZYMOGEN GLYCOGEN SYNTHASE - Is the inactive precursor of a proteolytic - An enzyme involved in the synthesis of enzyme. glycogen is deactivated by phosphorylation.